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2021's Weather Happenings
Marches of 19th Century Were Far More Wintry Than They Are Today

A Taste of Summer: The Year's First High of 80+

 First
Since 1980, the average date of the first reading of 80° or warmer is April 21 (a month later than the average date of the first reading of 70°+).  This is about a week earlier than 1900-1979, and two weeks earlier than the 1869-1899 period.  It's happened as early as March 13 (in 1990) and as late as June 7 (in 1924).  1918, 1927, and 2010 had their first reading of 80+ occur on the same date as each year's first high in the 90s. 

 

The average high temperature on the day before the first 80+ reading has been 70°, on the day of the first 80+, it's been 83°, and the high on the day following has averaged 74°. 

 

About one-third of the years have had a day of 80° or warmer on the day following the first 80+, but 16 years didn't have their second high of 80°+ for four weeks or more.  The greatest number of days to elapse before the second 80+ reading was 57 in 1928 (April 6-June 1).  The most recent lengthy hiatus was 41 days in 2013 (April 10-May 20).

 

Eight years have had their first 80+ high in March.  The first time it happened was in 1921, the most recent occurrence was 100 years later, in 2021.  Meanwhile, a first 80+ in June has occurred just once (1924).

 

Chart - earliest and latest first 80

 

On the day with the first high of 80° or warmer, the diurnal variation has averaged 27 degrees (this compares to a 14-degree variation for any day of the year).  The  greatest variation was 43 degrees in 1929, when the high/low was 89°/46°.   The smallest variation was 16 degrees in 1908 (81°/65°).

 

Chart - greatest diurnal variation on day of first 80
 

The chilliest low on the day of  the first 80+ reading was 43° in 1936 and, again, in 1990.  The warmest low was 68° in 1898.  The chilliest day-before high was 49°, in 1977.  The chilliest day-after high was 50° in 1921, and 51° in 1939.

 

29 years (about once every five years) had a warmer reading on the day after the first 80+ reading.  The warmest day-after reading was 93° in 1988.   The last time the day-after was warmer was in 2009, when the  high was 92° (the first 80+ reading that year was 88°).  The warmest day-before reading was 79°, which has happened in four years, most recently in 1955.  (And ten other years had a day-before high of 78°.)

 

April 19 is the date that's had the most first 80+ occurrences - in ten years.  And it's happened in seven years on April 25.   The most consecutive years to have the first 80+ occur in May is six, from 1873-1878. 

 

There have been six pairs of years in which the date of the first 80+ was the same:

> April 18, in 2015 and 2016

> April 15, in 2002 and 2003

> April 19, in 1972 and 1973

> April 26, in 1969 and 1970

> May 16, 1931 and 1932 (and in 1933, the date was 5/15)

> April 19, in 1914 and 1915

 

There have been fiver pairs of years in which the dates of the first 80+ were at opposite ends of the early/late spectrum.

> 1997 - May 19/ 1998 - March 27

> 1988 - May 23/ 1989 - March 28

> 1984 - May 23/1985 - March 29

> 1945 - March 20/ 1946 - May 25

> 1920 - May 28/ 1921 - March 21

 

Finally, measurable rain has fallen on the day of the first 80+ reading in 20% of the years (similar to the day of the first reading of 70+).  The biggest rainfall on this date was 0.67" in 1984 (May 23) as afternoon thunderstorms moved in after the temperature peaked at 81°; the second most was 0.60" in 1951 (4/29).

  80 plus

 

 

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